The present invention provides an improved valve stem seal and more particularly to a valve stem seal having a pumping action for oil to lubricate the valve stem in its associated guide.
An internal combustion engine includes a plurality of intake and exhaust valves, each valve comprising a valve head received in a valve seat defining an intake or exhaust passage and an elongated stem reciprocably mounted in a valve guide formed in the cylinder head of the engine. The end of the valve stem remote from the head is engaged by a rocker arm in an overhead valve engine or by a cam-operated plunger in an L-head engine. Oil is generally supplied to the upper end of the stem through an oil splash system or by a localized oil supply through the rocker arm to the point of contact with the end of the valve stem so that lubrication is present between the valve stem and its associated guide.
Oil is also present in the upper cylinder area of overhead cam engines due to slow oil draindown at higher engine speeds and camshaft lubrication. This oil floods the upper valve seal area, making umbrella-type seals inefficient in overhead cam engines.
In order to reduce oil consumption and provide optimum engine performance, a seal has been provided for the valve stem ranging from the umbrella-type shield utilized to deflect the majority of oil away from the upper end of the valve guide to a seal closely conforming to and engaging the valve guide boss and valve stem to restrain all oil flow to the valve stem save a thin film acting as a lubricant for the stem in the guide. However, many of these metering-type seals were ineffective and either dried out during use so that no oil was metered or, because of wear, allowed an excess of oil to enter the valve guide. The present invention obviates these problems by providing a valve stem seal with a positive pumping action.
The present invention comprehends the provision of a valve stem seal formed of two parts; the part engaging the valve stem formed of an elastomeric material closely embracing the valve stem and tending to prevent capillary flow therebetween. The outer seal part is formed of a relatively inflexible material and is provided with a cylindrical wall or skirt encompassing the valve guide boss and a radially inwardly offset cylindrical wall at the upper end provided with a radially inwardly extending annular flange adapted to be received in an annular groove in the resilient valve seal part that engages the valve stem. The annular flange has metering grooves on the upper and lower surfaces thereof cooperating with the flexing of the insert or collar during reciprocation of the valve stem to positively pump oil there along.
The present invention also comprehends the provision of a two-part valve stem seal wherein the seal body supporting the collar is formed of a relatively inflexible plastic material having a lower cylindrical wall fitting over the valve stem guide. The plastic bodied seal is designed to lock on an engine valve guide boss without conventional external retention rings.
The present invention further comprehends the provision of a two-part seal having a valve seal body and a resilient insert or collar providing the valve stem engaging surface. The metering area for the seal is external to the valve stem/seal interference area, thus eliminating a possible inconsistency of action found in positive type seals currently available.
Further objects are to provide a construction of maximum simplicity, efficiency, economy and ease of assembly and operation, and such further objects, advantages and capabilities as will later more fully appear and are inherently possessed thereby.